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Abstract
The target of this study is to develop isolates from the bioinsecticide B. thuringiensis var. kurstaki resistant to UV-irradiation with more pathological effect against the larvae of the house fly, M. domestica L. By exposure of the vegetative cells (normal culture) of Bacillus thuringiensis var. kurstaki to UV source with wavelength of 312 nm for 30 min. The UV-resistant colonies were isolated, and subcultured. This technique was repeated twice and the resulting three resistant isolates were designated as Btk-I, Btk-II and Btk-III, respectively beside Btk-N for the normal strain. The toxicity of non-irradiated and irradiated B. thuringiensis to 3rd larval instar of M. domestica were studied after feeding larvae on artificial media contaminated with different concentration of the bacterial samples at 28 oC.
The obtained results could be summarized as follows:
(1) Susceptibility of M. domestica to B. thuringiensis.
a- Susceptibility tests were performed using the food contamination method to estimate baseline level of susceptibility of the larvae to normal and UV resistant isolates of B. thuringiensis. The most effective isolate was Btk-III followed by Btk-I, Btk-II and Btk-N with the following LC50’s, 1.22, 14.26, 38.98 and 348.73 mg bacteria/100ml of the larval media, respectively.